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J Thorac Cardiovasc Surg 2007;133:577-578
© 2007 The American Association for Thoracic Surgery
Brief Communication |
John Radcliffe Hospital, Oxford, UK.
Received for publication September 8, 2006; accepted for publication September 28, 2006. * Address for reprints: Stephen Westaby, FRCS, MS, PhD, FETCS, FESC, FACC, FICA, John Radcliffe Hospital, Headley Way, Headington, OX3 9DU, Oxford, UK. (Email: swestaby{at}ahf.org.uk).
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Operations on patients with advanced heart failure carry substantial mortality, but this group has much to gain if they survive. Conventionally, the intra-aortic balloon pump (IABP) is used to assist weaning from cardiopulmonary bypass (CPB), but postischemic stunning may further impair myocardial function. This results in renal shutdown and deranged metabolic status. In established cardiogenic shock, attempted salvage with a left ventricular assist device (LVAD) carries a 50% to 75% mortality.1,2
To improve outcome in borderline survival situations, we decided to wean directly from CPB to a short-term centrifugal blood pump.
The patients at highest risk are selected before surgery. Candidates may have left ventricular ejection fraction less than 20%, impaired renal function, or aortoiliac disease precluding IABP use. LVAD implantation is undertaken during 30 minutes of reperfusion, before discontinuation of CPB. Conduits for the inflow and outflow cannulas are used to improve the safety of decannulation (Figure 1).
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The pump head priming volume is 31 mL. The system is filled during reperfusion and deairing of the native heart. When the patient is weaned from CPB, the LVAD provides 3 to 4 L/min flow. Antegrade cardiac ejection provides systemic pulsatility. Combined output from the device and the left ventricle is around 3.0 L/m2
· min. Transesophageal echocardiography confirms the position of the inflow cannula and the efficacy of deairing. After protamine, the sternotomy is closed to allow extubation during support. To minimize bleeding, no anticoagulation is given for 12 hours. Once the chest tube drainage is less than 50 mL/h, heparin infusion provides an activated partial thromboplastin time ratio of 1.5 to 2.5. Myocardial function is assessed daily with pump flow turned down to 2.0 L/(m2 · min). Postischemic dysfunction normally resolves during 3 to 7 days. After sustainable improvement has been achieved, the pump is switched off, the cannulas are withdrawn, and the grafts are ligated close to their insertion.
Five consecutive case studies are summarized in Table 1. All patients had severe symptoms (New York Heart Association functional class IV) and were considered at high risk for conventional surgery. Patients 1, 2, 3, and 5 had an IABP during anesthetic induction. Patient 4 had aortoiliac occlusion. None required reentry for bleeding. After the operation, the IABP was kept in place for 24 to 36 hours after removal of the LVAD. Patients 2 and 4 required hemofiltration for renal impairment. There were no pump-related adverse events.
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All 4 patients who walked into the hospital were discharged. Each has shown marked symptomatic relief and improvement in left ventricular function.
Heart failure surgery is an evolving specialty in which risk management plays an important role. As risk profile increases, there is a need for reliable short-term circulatory support to contain mortality. The rationale for elective LVAD deployment is straightforward. The failing heart pumps more than 7000 L of blood per day against an increased afterload. A dilated heart has greater wall tension and increased myocardial energy demand but suffers reduced subendocardial blood flow. After surgery, ischemia-reperfusion injury may trigger the downward spiral into cardiogenic shock and multiorgan failure. Inotropic agents temporarily elevate systemic blood pressure, but they exert deleterious effects by increasing heart rate, afterload, and subendocardial ischemia.3 In contrast, the LVAD unloads the ventricle, boosts coronary and systemic blood flows, and promotes myocardial recovery. Some inotropic support may be required to sustain right ventricular contractility.
Conventionally, LVADs are deployed only when death appears certain, but established cardiogenic shock may not be reversible.1,2 The willingness to use LVAD technology preemptively to prevent deterioration and promote recovery depends on the safety of the system, the requirement for technical support, and the cost. For recovery after ischemic arrest, the support duration is usually less than 7 days. In this time frame, the Levitronix pump is reliable, safe, and effective. It is readily managed by nursing staff and easily portable. Reoperation for bleeding and decannulation problems are avoided by the use of conduits.
To date this LVAD has been used in more than 300 patients for up to 64 days. The predominant indication (45%) has been salvage postcardiotomy support (mean of 9 days), with 53% survival. We suspect that the 47% mortality could be reduced by anticipating postoperative deterioration and using the blood pump electively to prevent cardiogenic shock.
References
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